Peracetic acid, sometimes called peroxyacetic acid or PAA, is a well known chemical for its strong oxidizing potential. Peracetic acid has a molecular formula of C2H4O3 or CH3COOOH, a molecular mass of 76.05 g/mol, and a molecular structure as follows:

Peracetic acid is a liquid with an acrid odor and is normally sold in commercial formulations as aqueous solutions typically containing, e.g., 5, 15 or 35 wt % peracetic acid. Such aqueous formulations not only contain peracetic acid but also significant concentrations of hydrogen peroxide and acetic acid, in a dynamic chemical equilibrium.
Aqueous solutions of peracetic acid, diluted to concentrations below 5 wt % peracetic acid, are widely used in a variety of end use applications for their wide spectrum antimicrobial and biocidal properties, as bactericides, fungicides, disinfectants and sterilants, and also for their bleaching properties. Aqueous peracetic acid exhibits antimicrobial activity that is more potent than aqueous hydrogen peroxide at equivalent low concentrations. A good overview of peracetic acid and its commercial antimicrobial applications is given by M. Kitis in “Disinfection of wastewater with peracetic acid: a review” Environment International 30 (2004) 47-55.
Aqueous peracetic acid solutions have had limited use in commercial well drilling operations, and only a few uses in this application are described in the literature.
Peracetic acid has been described as a bactericide for use in water, called flood waters, used in secondary oil recovery, in U.S. Pat. No. 3,329,610 of Kreuz et al., the disclosures of which are hereby incorporated by reference. Besides the peracetic acid bactericide, the only other component present in the flood waters is a standard corrosion inhibitor, e.g., a mixture of fatty acid alkylolamide, amine sulfonate, glycerine and diethanolamine sulfonate (Example 3).
Another use for peracetic acid is well cleaning described in U.S. Pat. No. 3,470,959 of Kreuz et al., where peracetic acid is added to water (normally potable water) that is injected into so-called recharge wells that are used in conjunction with the removal of potable water from coastal underground potable water basins.
Peroxyacetic acid used in synergistic combination with a phosphonium salt compound has been described as an antimicrobial combination, in PCT International Patent Publication No. WO 2000/04777 of ECC International, primarily for use in industrial water treatments such as pulp and paper or cooling tower operations. The synergistic antimicrobial combination is described as being generally useful in a broad spectrum of end use applications, one of which mentioned is controlling microorganism contamination in oil-field drilling fluids and muds, and in secondary petroleum recovery processes (pages 4-5).
In another application in oil and gas well operations, peracetic acid and hydrogen peroxide are described as useful, in buffered solutions, for improving the permeability of wells containing polymer deposits by removing the polymer deposits, in U.S. Pat. No. 7,156,178 of Rae et al.
The use of buffered peracetic acid solutions of Rae et al. in U.S. Pat. No. 7,156,178 for removing polymer deposits underscores an apparent disadvantage of using peracetic acid as a biocide in commercial oil- and gas-field operations. Commercial peracetic acid solutions also contain significant concentrations of hydrogen peroxide, a strong oxidizer, which can degrade useful polymer additives also present in aqueous fluids used in commercial well drilling, recovery or production applications.
Several biocides are currently used in oil- and gas-field operations, the most commonly used being glutaraldehyde (also called 1,5-pentanedial) and tetrakis hydroxymethyl phosphonium sulfate (often abbreviated as THPS).
In oil- and gas-field operations, polymer additives have been widely used for decades to enhance or modify the characteristics of the aqueous fluids used in well drilling, recovery and production applications.
One example of such use is for friction reduction in water or other water-based (aqueous) fluids used for hydraulic fracturing treatments in subterranean well formations. Hydraulic fracturing creates fluid-conductive cracks or pathways in the subterranean rock formations in gas- and/or oil-producing zones, improving permeability of the desired gas and/or oil being recovered from the formation via the wellbore.
“Slick water” fluids are water or other aqueous fluids that typically contain a friction-reducing agent to reduce frictional drag and improve the flow characteristics of the aqueous fluid being pumped via the well into the gas- and/or oil-producing zones, whether for fracturing or other treatments. The friction reduction agents are usually polymers, and the most commonly used for this purpose are polyacrylamide polymers and copolymers. These friction-reducing additives allow the water to be pumped into the formation more quickly.
Another example of polymeric agents' utility in oil- and gas-field well applications is for viscosity enhancement. Many aqueous fracturing fluids utilize natural or synthetic viscosity-increasing polymers, some of which are categorized as gelling agents. Examples of such natural and synthetic polymer additives in fracturing fluids include guar, xanthan, cellulose derivatives and polyacrylamide and polyacrylate polymers and copolymers, and the like. The gel-forming or thickening additives allow the aqueous well fluid to carry a significant amount of a proppant, typically an inorganic solids propping agent like sand, into the fractures and fissures in the formation without premature settling of the proppant.
The present invention provides a peracetic acid biocide that is useful in aqueous fluids for oil- and gas-field operations and that is not deleterious to the viscosity-modifying polymer additives present in such aqueous treatment fluids.